Mexopencv is a software package that provides Matlab mex functions that interface over a hundred of OpenCV functions. You can find it here. For a full list of supported OpenCV functions, see this page.

Installation is easy, just follow these steps (assuming that you already installed OpenCV).

1. Make a directory where you want to install mexopencv
mkdir <installation_dir>
cd <installation_dir>
2. Get the source-corde using git. If git is not installed yet, get it from the repository.
git clone git://github.com/kyamagu/mexopencv.git
3. Compile the code, make sure that your Matlab directory is given correctly. This is needed because the Makefile uses the mex compiler.
cd mexopencv
make MATLABDIR=/usr/local/MATLAB
4. Thats it. To use this functions make sure that the path is included in Matlab. This is easily done in the Matlab command window:
addpath('<installation_dir>/mexopencv')
5. Now you can use all the functions in Matlab. For example to rescale an image:
% Set the resize factor
resize_factor = 0.8;
% Read an input image using Matlab
input_image = imread('image_name');
% Rescale the image using OpenCV
resized_image = cv.resize(input_image, resize_factor);